The present invention relates to an apparatus using charged particle beam with a sample stage drive device on which a sample to be measured including observation thereof is mounted, and, in particular, relates to an apparatus using charged particle beam such as a scanning type electron microscope which is suitable for automatic observation of a sample with such as a scanning type electron microscope and an optical type microscope, of which configuration, internal structure or location is known in advance.
It is already known a few methods in which when observing with a scanning type electron microscope a sample of which configuration, internal structure or location is known in advance, drawings or photographs showing the same and coordinate used for designating position of observation portion in the sample are related with displacement of a sample stage with some proper measure and a portion on the sample desired to be observed is quickly and automatically displaced in a simple manner into a visual field. Among these methods a method, for example, disclosed in U.S. Pat. No. 4,814,682 is one of effective ones. The disclosed method is intended to reduce workload for observation by manually designating position of a portion desired of observation, however, in a current scanning type electron microscope the disclosed method is further advanced and an automatic designation through a computer is performed. Currently, the method is used for the purpose of observing a microscopic pattern desired to be observed existing in a chip which can not discriminate and recognize on a chip design sheet while assuming respective chips, which are formed in a plurality of pieces on a common supporting body called as a wafer with a same design pattern and with a geometrical location relationship with a predetermined accuracy, as respective samples.
After once mounting actually a wafer on a sample stage, the position where the wafer is fixed temporarily on the sample stage at this instance is assumed as a reference position for observation position designating coordinate on the wafer. A control device for the scanning type electron microscope virtually registers the plurality of chips in a grid shape on the wafer according to the coordinate at this instance while framing such as the chip size, location and rotation direction in the wafer plane in a square chip outer configuration in a relationship based on the chip design data. By making use of the grid coordinate values of observation pattern, portions within a chip are thereafter determined.
Under a condition where a sample is actually mounted on a sample stage, the sample stage is displaced manually while observing the sample with the scanning type electron microscope and the position of a portion designed to be observed is manually designated in advance on the actual sample. The control device for the scanning type electron microscope determines the position of the portion desired to be observed after converting the same into a coordinate value within the chip from the coordinate value of the sample stage at the moment and the chip alignment, and stores the same together with the scanning type electron microscope image of the observed portion while relating thereto. Thereby, for the subsequent observation the control device for the scanning type electron microscope determines a coordinate value of a position to which the sample stage is to be automatically displaced from the coordinate value within the chip of the position for the observation portion and the chip alignment position registered in advance, and further performs an automatic identification of the observation portion through a picture image collation with the image of the observation portion which is stored while relating to the observation portion.
In the above U.S. Pat. No. 4,841,682, before performing an observation with respect to two portions on the actual sample among any portions showing characteristic sample structures the positions based on the design data on the drawing sheet and the position on the actual sample are related, thereby coordinate calibration is performed between the sample stage coordinate and the coordinate on the sample drawing sheet, in that the coordinate used by a coordinate designation means. As a result, when a position of a observation portion is designated by the coordinate designation means thereafter, the observation position can be brought into a visual field with a predetermined accuracy. In particular, when samples which permit designation of an observation position on a same design sheet are mounted on the same supporting body (for example, IC patterns arranged on a sample stage for a pattern comparison), through a provision of a switching function by a sample selection switch, the designation of observation positions of plural samples can be enabled by the same drawing sheet.
In the above U.S. Pat. No. 4,814,682, a sample (IC pattern) arranged on a common supporting body (sample stage) was an object for observation, however, in a recent scanning type electron microscope used for semiconductor manufacturing processes the object for observation is being replaced to a combination of IC patterns arranged on a wafer. Herein, the designation of two characteristic points is not limited on the same sample (the same chip), but is permitted over a plurality of samples (a plurality of chips). Therefore, coordinate on the coordinate designation means which can cover the entire samples located is set and then coordinate calibration between the coordinate on the coordinate designation means and the sample stage coordinate is performed. In such instance, since the plurality of samples (the plurality of chips) are located geometrically on a common supporting body (a wafer) with a predetermined accuracy, an observation position (x, y) can be determined from chip alignment pitch (px, py), chip location (nx, ny) and in-chip position (xd, yd) according to the following equation (1);                                                                         x                =                                                      px                    xc3x97                    nx                                    +                  xd                                                                                                        y                =                                                      py                    xc3x97                    ny                                    +                                      y                    ⁢                                          xe2x80x83                                        ⁢                    d                                                                                      }                            (        1        )            
In this method, as a preparation before observation, registration of two portions having characteristic structures is performed. Namely, with reference to the mounted position of the wafer on the sample stage at this moment a two dimensional coordinate designed by two characteristic portions on the mounted wafer is prepared as designated coordinate on the coordinate designation means. On this coordinate a drawing used in the coordinate designation means is prepared from an arrangement of a grid representing such as a chip size and chip location which are defined according to the design data. When observing in subsequent observations another wafer locating totally identical samples (chips) and being mounted on the sample stage, the position for the observation portion on the sample stage is designated based on the above designation coordination. However, the mounting position of a wafer on the sample stage is determined by mechanical contact between the sample stage and the wafer, therefore, a small amount of deviation is caused from the instance when registering the two characteristic portions previously, and the deviation amount varies every observation. In order to correct such deviation, the positions of the two same characteristic points located at the same positions as those registered previously are compared with the positions registered first to thereby perform coordinate calibration. Thus, coordinate calibration between the coordination at the time of registration giving the coordination of the coordinate designation means and the sample stage coordination at the time of observation is performed. Further, the coordination calibration performed by correspondence between two points within the sample in U.S. Pat. No. 4,814,682 was applied to the coordinate representing a geometric location of a plurality of samples (chips) on a common supporting body (wafer) as well as to the coordinate representing the positions of observation portions within a sample (chip) as it is.
However, actually, in a course of printing chips (individual samples) on a wafer (a supporting body), in particular, during semiconductor manufacturing processes, a main factor which determines a positional accuracy of chip alignment on a wafer depends on a positional accuracy of the sample stage in a printing device (hereinafter called as a stepper), on the other hand, a main factor which determines a positional accuracy of observation portions within a chip depends on distortion of a stepper lens. Further, when designating the chip alignment by a single point in the respective chips, a deviation of the sample stage coordinations with in-plane rotation direction of a plane coordinate of respective entire chips causes a same effect when the positions of the observation portions within a chip are deviated. In particular, when observing a portion different from the portion which was used for the coordinate calibration, the deviation will be increased as the distance from the coordinate calibration position increases due to the entire chip rotation, which shows that only with the measure of the coordinate calibration with respect to the coordinate for the set of the coordinate designation means, it is impossible to bring about a visual field of an observation position by the coordinate designation with a sufficiently high positional accuracy, because of the different factors determining the positional accuracy of the both. However, such positional deviation at the time of bringing about a visual field frequently shows a certain tendency with regard to deviation direction and amount, when such visual field bringing about operation by the sample stage displacement is performed several times at the sample positions. Namely, it frequently happens that stop positions for actual visual field collectively appear around a position spaced apart some from a target position in a certain direction, which shows a state representing xe2x80x9ca low positional accuracy but a good positional reproducibilityxe2x80x9d.
Further, on the other hand, when displacing a sample stage for respective observation devices, it is frequently caused respective positional deviations inherent to the individual observation devices. For example, FIGS. 17 and 18 show respective examples of positional accuracy of the sample stage for devices A and B. The drawings show loci of actual stage displacement which are determined by measuring respective crossing points on the grids, when the stages are displaced along a straight line on the two dimensional plane. When comparing the both devices, the positional deviations at respective crossing points with respect to respective target positions are not the same in connection with both direction and amount thereof. Further, it is observed even with the same device the deviations are different depending on the target positions.
Although these deviations depend on a direct operation performance of such as a direct operation guide constituting such stages, it is difficult to produce a guide which performs a complete direct operation. Therefore, when displacing a visual field of a microscope through displacement of such stage, and if it is intended to locate a target position on a sample at the center of the visual field, a positional deviation from the center of visual field is inherently caused.
However, such positional deviation at the time of bringing about a visual field frequently shows a certain tendency with regard to deviation direction and amount, when such visual field bringing about operation by the sample stage displacement is performed several times at the sample positions. Namely, it frequently happens that stop positions for actual visual field collectively appear around a position spaced apart some from a target position in a certain direction, which shows a state representing xe2x80x9ca low positional accuracy but a good positional reproducibilityxe2x80x9d.
Among two factors of the positional deviations, one caused by the sample and the other caused by the sample stage of a microscope, when one or two are caused at the same time, the positional deviation at the time of bringing about a visual field can be caused. However, regardless that the positional deviation may be caused by either or both of the factors, it will be understood that the state representing xe2x80x9ca low positional accuracy but a good positional reproducibilityxe2x80x9d is obtained.
Until now, in order to correct such positional deviation, several methods of coordinate calibration between the designation coordinate of an observation position and the stage coordinate serving as a reference at the actual displacement have been proposed.
One of the examples is that instead of displacing the stage with reference to the dotted lines in FIG. 17 or FIG. 18, when designating an actual displacement to the stage, the displacement distance is determined with reference to the solid lines to provide the designation value. Since the solid lines show a manner that which the stage is actually displaced, displacements near the crossing points at respective grids show respective effects of certain extent. However, positions remote from these crossing points, for example, any points near the position of the center of gravity are spaced apart from all of the calibration points, therefore, in actual sense a correct calibration is not necessarily performed for the positions. In this instance, if the sides of grids are infinitely reduced, the number of the calibration points increases and the distance therebetween shortened. Therefore, the distance to calibration points from any points are reduced, thereby, the above referred to problem is resolved to a certain extent. However, when increasing the grid points, in that the calibration points, it is necessary to perform many registrations depending on number of the calibration points and when in view of the calibration work which has to be performed by an operator, an increasing of the grid point number has to be limited.
Such phenomenon was actually confirmed that when the visual field is brought about in a scanning type electron microscope with the conventional method, the amount of visual field deviation increases as the observation position is away from the two characteristic points used for the coordinate calibration.
Until now, when such deviation amount is large, in order to cope with such circumstance an image magnification rate of a scanning type electron microscope image is reduced to ensure a broad search area when performing a positional search by means of a picture image collation by making use of a scanning type electron microscope image of the observation portion. However, with this measure it is necessary to perform the picture image collation for all of many objects appearing in the broad area which requires long search time. Further, as one of inherent characteristics of a scanning type electron microscope, when performing an image observation with a low magnification rate, it is likely affected of an image disturbance due to such as charge-up caused by primary electron irradiation, and the scanning type electron microscope image is likely unstabilized which causes a problem of frequent erroneous searches due to erroneous recognition.
Since the magnification for the observation of a scanning type electron microscope which is used these days in a semiconductor manufacturing processes for observation use is high, it is necessary to displace the sample stage with a high positional designation accuracy, in order to bring about an observation object into a visual field. On the other hand, the scanning type electron microscope is required to be operated in a high operation efficiency as well as to perform a process management through an automatic observation.
The present invention is achieved in view of the conventional problems, and an object of the present invention is to provide an apparatus using charged particle beam such as a scanning type electron microscope which is used for observing faulty chip patterns, in particular, during semiconductor manufacturing processes and which permits quick and accurate displacement of an observation position into an observation visual field.
An apparatus using charged particle beam according to the present invention is provided with means for detecting positional difference between a target position on a chip pattern within an observation visual field of a microscope after displacing a sample stage thereof and a predetermined position within the visual field, means for storing the detection result and means for determining a new displacement target position for displacement to the predetermined position in subsequent observation while taking into account the positional difference stored previously and the displacement target position used at the time of storage.
In another aspect of the present invention, through provision of means for detecting positional difference between a target position on a chip pattern within an observation visual field of a microscope after displacing a sample stage thereof and a predetermined position within the visual field, means for determining a new displacement target position while correcting a displacement target position used at the moment by making use of the detection result, means for storing the new displacement target position at every determination and means for determining a new displacement target position for displacement to the predetermined position in subsequent observation while taking into account the after correction displacement target position stored previously.
When observing another wafer on which the same patterns with the same alignment as the previous one are printed or another pattern on the same wafer, the previous sample stage displacement target designation position is also modified while taking into account of the previous observation visual field position deviation which is registered to the corresponding observation position, and the stage is displaced according to the designation position.
A coordinate on a coordinate designation means for designating a position within a sample, in that a chip (which is hereinafter called as in-sample position designating coordinate) and a coordinate on the coordinate designation means for designating a chip alignment are separately provided (which is hereinafter called as alignment position designating coordinate). These sample stage coordinates give ones with reference to a fixed position with respect to the sample stage of the samples, in that chips and a supporting body, in that a wafer, mounting a plurality of the samples at the moment of registering two characteristic structures which are used for coordinate calibration performed prior to the observation and using the characteristic structures, and the ones using an arbitrary position on the wafer as an origin. However, when a wafer is again remounted on the sample stage for observation after the two portions have been registered, a deviation from the original position is caused because of limitation in mechanical origin matching accuracy between the wafer and the sample stage. In such instance, a deviation amount of a desired position for observation portion from the concerned portion after completing sample stage displacement is detected, the deviation detection result or corrected displacement target position using the result is successively stored, then, statistical processing result of these past deviation amount or the after correction displacement target positions are reflected on a newly determined displacement designation position, or re-determination of displacement designation position is performed based on these results.
On one hand, when performing an automatic observation, these positional deviation amounts are recorded in advance in the sequence file recording observation sequence including observation position while relating to the observation position. When performing an observation according to the sequence file, the positional deviation amount is reflected to the displacement designation position. The method of the reflection is as same as the one explained above. On the other hand, the microscope device, in which the positional deviation recorded in the sequence file is caused, is separated from other microscope devices. For the separation, for example, the manufacturer""s serial number of the device is recorded together with the detected positional deviation amount.
After having prepared the sequence file and when the sequence file is used for another device, the device automatically reads the manufacturer""s serial number and also automatically identifies the device in which the detected positional deviation is resulted. The displacement designation position is determined while only taking into account of the records of the positional deviation amounts or of the displacement target positions which are corrected every time by making use of the result of these positional deviation amounts which are confirmed as those of the concerned device. Thereby, a possible correction by making use of positional deviation detected in other device can be prevented. With the above measure, even under a circumstance where the observation sequence file is exchangeably used between different devices, a sample stage with a high positional designation accuracy can be provided.
Namely, the apparatus using charged particle beam according to the present invention, which comprises a charged particle beam source for generating charged particle beams; a sample stage which holds a sample and displaces the same; a lens which converges charged particle beams emitted from the charged particle beam source onto the sample; a deflector which deflects the charged particle beams; a picture image detection means which detects a picture image of the sample; a picture image display means which displays the picture image detected; a coordinate designation means which designates a position on the sample; means for relating a coordinate value on the coordinate designation means to a coordinate value on the sample stage while permitting calibration thereof and for displacing the sample stage to a position of the sample stage corresponding to the coordinate value designated on the coordinate designation means, is characterized in that the apparatus further comprises, a positional deviation amount calculation means which, when observing any observation position on the sample, displaces the sample stage so that a displacement target position designated by the coordinate designation means coincides with the observation position and calculates a positional deviation amount between a predetermined position on a sample which is detected by the picture image detection means after completing the displacement and a predetermined position of the picture image detection means; a memory means which stores the calculated positional deviation amount; and a positional deviation correction means which controls a displacement target position coordinate value used when displacing subsequently to an observation position corresponding to the previous observation position or the same observation position based on the positional deviation amount determined by the positional deviation amount calculation means and operates so that the predetermined position of the sample at the time when the sample stage stops and the predetermined position on the picture image display means coincide each other.
With the apparatus using charged particle beam according to the present invention, since the sample stage displacement target position is determined while taking into account in advance of the visual field deviation amount caused in the course of displacement to the position prior to the concerned observation, the stop position accuracy of the sample stage can be enhanced.
Further, the apparatus using charged particle beam according to the present invention, which comprises a charged particle beam source for generating charged particle beams; a sample stage which holds a sample and displaces the same; a lens which converges charged particle beams emitted from the charged particle beam source onto the sample; a deflector which deflects the charged particle beams; a picture image detection means which detects a picture image of the sample; a picture image display means which displays the picture image detected; a coordinate designation means which designates a position on the sample; means for relating a coordinate value on the coordinate designation means to a coordinate value on the sample stage while permitting calibration thereof and for displacing the sample stage to a position of the sample stage corresponding to the coordinate value designated on the coordinate designation means, is characterized in that the apparatus further comprises, a positional deviation amount calculation means which, when observing any observation position on the sample, displaces the sample stage so that a displacement target position designated by the coordinate designation means coincides with the observation position and calculates a positional deviation amount between a predetermined position on a sample which is detected by the picture image detection means after completing the displacement and a predetermined position of the picture image display means; means for determining after-correction displacement target position coordinate value after correcting the displacement target position coordinate value used at the moment by making use of the calculated positional deviation; a memory means which stores the determined after-correction target position; and a positional deviation correction means which controls a displacement target position coordinate value used when displacing subsequently to an observation position corresponding to the previous observation position or the same observation position based on the after-correction displacement target position coordinate value stored in the memory means and operates so that the predetermined position of the sample at the time when the sample stage stops and the predetermined position on the picture image display means coincide each other.
The apparatus using charged particle beam according to the present invention can further be provided with an observation sequence memory unit which stores such as a planed observation position, an observation portion picture image and an observation sequence and further stores the positional deviation amount or the after-correction displacement target position coordinate value while relating to the planed observation position coordinate value in the observation sequence memory unit.
Through the registration and storage of the record of the visual field deviation amount or the displacement target position corrected by the visual field deviation amount together with the observation sequence record as has been explained above, the present invention can provide a simple and proper method when repeatedly observing patterns on a same wafer or likely when repeatedly observing patterns on the same type of wafers.
Further, in the present invention, when controlling the displacement target position coordinate at the time of displacing to an arbitrary observation position, a statistically processed result of the positional deviation amounts or the after-correction displacement target position coordinate values for a plurality of times obtained previously can be used. The statistical processing can be an averaging processing. Further, the statistical processing can be a weighted averaging processing in which the positional deviation detection result obtained lately is heavily weighted. When processing the past visual field deviation amounts through the statistical processing method including the averaging and weighted averaging in which the latest amount is heavily weighted, the stop position accuracy of the sample stage can be stabilized with a high accuracy.
Further, in the present invention, means for setting in advance an effective number of traceable past positional deviation amounts calculated by the positional amount calculation means can be provided. Further, means for storing the effective number of the traceable past positional deviation amounts calculated by the positional deviation amount calculation means while relating in advance with the observation sequence memory means can be provided and only the positional deviation amount calculation result corresponding to the calculation point number set for the automatic observation can be determined valid.
By limiting the useable number of visual field deviation amounts or of displacement target positions corrected by the visual field deviation amounts at a predetermined number as has been explained above, a necessary storage capacity can be properly suppressed.
Further, in the present invention, a device identification means can be provided which identifies an apparatus using charged particle beam for which the positional deviation amount or the after-correction displacement target position coordinate value has been obtained, the positional deviation amount memory means or the after-correction displacement target position coordinate value memory means stores the positional deviation amount or the after-correction displacement target position coordinate value for every apparatus using charged particle beam identified by the device identification means while relating to the planed observation position, and when determining the displacement target position of the sample stage by the positional deviation correction means, the displacement target position of the sample stage can be determined based on the statistically processed result of the detected positional deviation amount or the after-correction displacement target position coordinate value reflected by the detected positional deviation amount.
Through the provision of device identification marks for identifying scanning type electron microscopes, a common observation sequence can be used between different devices.
In the present invention, means for switching the positional deviation correction means between valid and invalid can be provided. Further, means for storing the setting between valid and invalid of the positional deviation correction means while relating in advance with the observation sequence memory means can be provided and the valid and invalid of the positional deviation correction means at the time of automatic observation can be controlled.
In the present invention, means for switching the positional deviation amount calculation means between valid and invalid can be provided. Further, means for storing the setting between valid and invalid of the positional deviation amount calculation means while relating in advance with the observation sequence memory means can be provided and the valid and invalid of the positional deviation amount calculation means at the time of automatic observation can be controlled.
Further, the apparatus using charged particle beam according to the present invention, which comprises; a sample stage which can displace in two dimensional direction; a coordinate value designation means which designates a position on a sample; means for relating a coordinate value on the coordinate value designation means to a coordinate value on the sample stage while permitting calibration thereof and for displacing the sample stage to a position of the sample stage corresponding to the coordinate value designated on the coordinate value designation means, is characterized in that the apparatus further comprises, a target position deviation detection means for detecting in a microscope visual field a positional deviation amount between a target position designated by the coordinate value designation means and a position after displacement of the sample stage; a positional deviation amount memory means for storing the positional deviation detection result by the position deviation detection means while relating to the target position; and a position deviation correction means which determines a displacement target position of the sample stage based on a statistical processing result of the positional deviation detection result relating to the concerned target position stored previously in the positional deviation amount memory means when designating the target position by the coordinate value designation means and displacing the sample stage to the target position.
The above apparatus using charged particle beam determines the sample stage displacement target position while taking into account in advance of the visual field deviation amount caused when displacing to the concerned position prior to the observation, therefore, the stop position accuracy of the sample stage can be enhanced. The target position deviation detection means can be realized by a length measurement function which measures distance between two points on an image of the apparatus using charged particle beam obtained at the time of observation. The apparatus using charged particle beam according to the present invention shows a characteristic that the positional deviation designated by the coordinate value designation means and the position after displacement of the sample stage is gradually reduced, as the displacement of the sample stage is repeated.